You are studying two proteins in E. coli. You notice that a mutation that leads

Question

You are studying two proteins in E. coli. You notice that a mutation that leads to a truncated protein 1 (due to a premature stop codon) also down-regulates expression of protein 2. Upon further investigation, you find that the genes for protein 1 and 2 are in tandem and transcribed as a single polycistronic RNA. Provide a potential mechanism as to how a stop codon in the first gene downregulates translation of the second. Propose two experimental procedures that you could perform to verify your explanation.

Explanation / Answer

Since there is a single polycistronic RNA for the two proteins this is a case of an operaon. The first protein might be acting as an activator for the operon like catabolite activator protein or CAP   which binds a sequence of 16 base pairs upstream of the promoter, thus inducing expression of the gene. Experimenting with mutants for protein 1 and wild type protein 1 can confirm the claim.

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